This invention relates to x-ray inspection, and more particularly, to a novel blackline indicator which can be radiographically imaged through a weld joint to facilitate determination and control of x-ray inspection system set-up parameters to provide appropriate spatial resolution and clarity for inspection of the weld joint to detect voids or other defects in the weld joint.
In tomographic and/or radioscopic inspection of a weld joint between two abutting pieces of material it is important to obtain parallelism between the x-ray beam central ray and the faces of the abutting pieces of a completed weld joint. This geometric alignment is critical because a misbond or lack of fusion at either or both side edges of the weld joint could escape detection if the x-ray beam were not precisely aligned with the joint and able to image the difference in thickness between a misbonded location and a properly fused location in the weld joint as seen along the x-ray beam path.
A presently used procedure for inspecting a weld joint between two components, such as two cylindrically shaped shafts which are butted end to end and welded together at their abutting faces, involves tack welding the two abutting faces at a plurality of locations around the circumference of the two shafts. A reference datum, such as a shoulder block or collar, which can be radiographically or radioscopically imaged with the joint, is required on one of the shafts at a predetermined distance from the tack welded joint. If a shoulder or similar feature is not already present, which may be used as a datum, such a surface feature must be attached to one of the shafts. The tack welded joint is then x-rayed to provide a radiographic image to verify the alignment of the x-ray beam relative to the plane of the tack welded joint. When the gap or "blackline" between the two abutting faces of the shafts are properly imaged with appropriate clarity and spatial resolution, the precise x-ray geometric set-up and parameters used to provide this image will be used for the actual weld joint inspection after the weld joint has been completely welded. The reference block or collar is used to properly position and align the finished weld joint within the x-ray fan beam for final inspection. After final x-ray inspection, the reference block or collar must be removed. This procedure, therefore, requires additional steps in order to properly inspect the weld joint. For example, the reference block or collar must be attached; the joint must be tack welded and radiographically imaged to provide a pre-inspection or "blackline" image to verify proper set-up of the x-ray system to provide appropriate x-ray inspection images with adequate spatial resolution after the final welding operation; and the reference collar or block must be removed. These additional steps reduce the cycle time and increase the expense of inspecting the component.
Additionally, if radioscopic images of the interior of the welded joint are desired, a "blackline" image may not be useful or appropriate for determining the appropriate x-ray system parameters or computed tomography (CT) parameters because of the close proximity of the x-ray source relative to the weld joint and because of the dynamic nature of the inspection process in which the x-ray source and detector or the weld joint are moved relative to one another to permit gathering of the data to provide the CT image.